Mohawk View Water Treatment Plant - Filter Failurenysawwa.org/docs/pdfs/5B-When Water Filters...

A Case Study of

Latham Water District’s

Mohawk View Water Treatment Plant - Filter Failure

Outline The Mohawk View Water Treatment Plant & 2005

Expansion

What Happened?

2010 Failure and Subsequent Failures

Investigation of the Failure

Remediation & Repair

What We Learned

Q&A

The Mohawk View Water Treatment Plant

Today

2005 2006 2007 2008 2009 2010 2011 2012 2013 2014

Plant Expansion to 31.5 MGD - Rebuilt Filters 1 - 6 - New Filters 7 - 10

Timeline

The Mohawk View Water Treatment Plant EXPANSION

Capacity: 31.5 MGD

2005: Completed $24 Million Expansion

• 4 New Dual Media Filters

• 6 Existing Filters Rebuilt

• All Filters Had Under Drain Systems and Utilized Filter Media Support Caps

Filter Cross Section

ORIFICE PLATE

Orifice Plate

Mechanically attached to the old tank wall

Integral connection between old and new

Under Drain Block

Media Support Cap

Underdrain Block

Today

2005 2006 2007 2008 2009 2010 2011 2012 2013 2014


All appears fine...making water

Grout Repairs in Filters 7 & 8 - Manufacturer

Representative instructs operators on repair techniques

- Repairs went well

Timeline

Today

2005 2006 2007 2008 2009 2010 2011 2012 2013 2014





- Repairs went well

Media loss observed in Filter 4 - Underdrain uplift noted - Manufacturer notified

Timeline

Initial Inspections by Plant Block Connections Broke O-Rings Exposed

Today

2005 2006 2007 2008 2009 2010 2011 2012 2013 2014





- Repairs went well


May 2011 – Media removed from Filter 4

June 2011 – Manufacturer site visit & inspection of failure

July, 2011 – Manufacturer’s report - Rebuild Filter 4 with new

underdrains - Town decides to have an

independent review of the failure

Timeline

Manufacturer’s Initial Inspection


Buckled underdrain system

Damaged grout and block connections


• A split media support cap was found at the back end of the filter

• No noticeable leaks

were found where the media support cap attaches to the underdrain blocks

Manufacturer’s Inspection Conclusions

• Leaks along orifice plate allowed media to enter underdrain

• Not much media inside laterals away from failure point

• Media support caps hydraulically tested – pressure drop in “normal range”

• Media under caps only where cap was split

• L-rod installed improperly … no epoxy, easily pulled out of the tank floor

Manufacturer’s Recommendations

REBUILD FILTER

• Remove all underdrains and base grout

• Backwash and flush all media from filter #4 flume and piping

• Remove and clean & reinstall the orifice plate

• Install new underdrain

• Test new system and re-install media

Today

2005 2006 2007 2008 2009 2010 2011 2012 2013 2014





- Repairs went well







B&L begins investigation of filter failure

Timeline

Filter Investigation

Determine the Cause of Filter 4 Failure

Assess Potential for Other Filters to Fail


Backwash Observations:

Continued air release during

High Rate Wash

Significant Boils along

Gullet wall


Air vent during water wash

Air must vent through underdrains

Air line installed low

Filter Investigation No caulk evident at orifice – wall interface

Orifice fasteners found loose

Seal at Orifice Plate

Misplaced Caulk

Filter Media in Effluent Flume

Filter Media Escapes Filter Tank


From top of media support cap

From bottom of media support cap


Significant amount of GAC found under media support caps


‘Old’ Rough Existing Concrete

Exposed Orifice Plate

Failing Grout at Fillet

Filter Investigation Here is what happens when media builds up under media support caps. Filters 1 & 5 Shut Down

Filters 1, & 5 Media in Flume

Today

2005 2006 2007 2008 2009 2010 2011 2012 2013 2014





- Repairs went well








Media loss observed at Filters 1 & 5 Filters 1 & 5 shut down

Timeline

B&L Filter Investigation Conclusions Low air vent from flume results in boils and loss

of media during backwash

Media leakage around orifice plate resulted in

Media buildup under support caps

Excessive backwash cycle pressure

CATISTROPHIC FAILURE OF Filter 4 UNDERDRAIN STRUCTURE

Repair Filters 4, 1 & 5 as “Emergency”

Today

2005 2006 2007 2008 2009 2010 2011 2012 2013 2014





- Repairs went well









Emergency declared - Filters 1, 4 & 5 Fast-track rehab

initiated - Filters 2, 3 & 6 rehab also initiated

Timeline

Demolition

Filter 4 Rebuild

Re-installing Orifice Plate

Filter 4 Rebuild

Ready To Install Support System

Filters 1, & 5 Repair

Clean media out of flume and piping

Filters 1 & 5 Repair

Flush media from Underdrains

Filters 1 & 5

Filters 1 & 5 Repair

Filter Support Block Orifice Plate Interface

Filters 1, 2, 3, 5 & 6 Repair Seal at the orifice plate

Today

2005 2006 2007 2008 2009 2010 2011 2012 2013 2014





- Repairs went well









Emergency declared - Filters 1, 4 & 5 Fast-track rehab

initiated - Filters 2, 3 & 6 rehab also initiates

Filter 5 back on line 6/21/13



Timeline

Filters 2, 3, & 6 non-emergency rehab complete

Monitoring of Future Problems

Monitoring Backwash Pressure

What Was Learned ‘Institutional Knowledge’ Has Left The Building

retirement of key workers

Do Not Underestimate Apparently Small Problems

track down problems to their root cause

relentless attitude is needed when problems arise

Get Others Involved Early

Design Engineers

Manufacturers

“It’s the little details that are vital. Little things make big things happen.” John Wooden

Mohawk View Water Treatment Plant - Filter Failurenysawwa.org/docs/pdfs/5B-When Water Filters...

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